<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" :ref="item" @touchstart="handleTouchStart"
            @touchmove="handleTouchMove" @touchend="handleTouchEnd" @click="handleLetterClick">{{ item }}</li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props: {
        cities: Object
    },
    computed: {
        letters() {
            const letters = []
            for (let i in this.cities) {
                letters.push(i)
            }
            return letters
        }
    },
    data() {
        return {
            touchStatus: false,
            startY: 0,
            timer: null
        }
    },
    updated() {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick(e) {
            this.$emit('change', e.target.innerText);
        },
        handleTouchStart() {
            this.touchStatus = true

        },
        handleTouchMove(e) {
            if (this.touchStatus) {
                if (this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                    const startY = this.startY
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - startY) / 20)
                    if (index >= 0 && index < this.letters.length)
                        this.$emit('change', this.letters[index])
                }, 16)


            }
        },
        handleTouchEnd() {

        },
    }
}
</script>

<style lang="stylus" scoped>
@import '../../../assets/styles/varibles.styl'
    .list
        display flex
        flex-direction column
        justify-content center
        position absolute
        top 1.58rem
        right 0
        bottom 0
        width .4rem
        .item
            line-height .4rem
            text-align center
            color $bgColor


</style>